The present invention relates generally to hyperthermia and, more particularly, to the use of electrodes internally placed in the vicinity of or inside of tissue to be heated in cooperation with an internally located receiver of radio-frequency energy for actuating pairs of electrodes, whereby an electric current flows between a particular pair of electrodes in such a manner that the tissue therebetween is heated and the temperature therein may be simultaneously automatically monitored during the procedure.
It is well known that elevating the temperature of tumors is helpful for reducing their size and tendency for metastasis. Modalities for applying heat to tumors include the use of direct contact radio-frequency (rf) applicators, microwave radiation, inductively coupled radio-frequency fields, ultrasound, and a variety of simple thermal conduction techniques.
Among the problems associated with all of these procedures is the requirement that highly localized heat be produced at depths of several centimeters beneath the surface of the body. Techniques have been developed whereby microwave radiation and ultrasound may be focused at various desired depths and radio-frequency applicators may be used at depth during surgery. However, the degree of localization is generally poor with the result that healthy tissue may be harmed. Induction heating gives rise to poor localization of the incident energy as well. That is, although induction heating may be achieved by placing an antenna on the surface of the body, superficial eddy currents are generated in the immediate vicinity of the antenna when it is driven using rf current, and unwanted surface heating occurs with little coupling to the underlying tissue. Thus, the currently employed, noninvasive procedures for providing heat to internal tumors, are incapable of doing so that substantial specificity and selectivity.
Another difficulty which arises as a result of the use of the above-described non-invasive techniques is the difficulty in the determination of the temperature of the heated tissues. Temperature awareness and control is of extreme importance during the administration of hyperthermia to internal body tissue since there is merely a small range of temperature which separates the destruction of tumor cells from the destruction of healthy tissue. Thermocouples and thermistors are commonly used to measure the temperature of the treated tissue, but they must be inserted into the vicinity of the tissue itself in order to produce accurate measurements, a process which may be traumatic to the patient.
Yet another problem with existing hyperthermia procedures arises if the patient requires more than one application of the procedure. This is often the case since many tumors can only be partially removed by surgical methods, and generally only temporary remission or tumor shrinkage results from a single hyperthermia treatment. Repeated applications would necessarily require surgery unless electrical leads are placed so as to emerge through the skin. The former situation might be at most repeated once or twice for a seriously ill patient if the tumor is located within a major body cavity, while the latter situation presents a significant risk of infection.
In "Method for Localized Heating in Tumor Tissue," U.S. Pat. No. 4,016,886, issued to Doss et al. on Apr. 12, 1977, the inventors describe a method for localized heating of tissue using radio-frequency currents applied directly to an exposed tumor which is effective only during the time that the tumor is accessible. This difficulty is partially solved according to the teachings of U.S. Pat. No. 4,448,198, "Invasive Hyperthermia Apparatus and Method," issued to Paul F. Turner on May 15, 1984. Therein the inventors describe the use of a plurality of needle-like electromagnetic energy applicators adapted for insertion into body tissue and radiating electromagnetic energy therein. A similar technique is described in U.S. Pat. No. 4,346,715, "Hyperthermia Heating apparatus," issued to Paul M. Gammell on Aug. 31, 1982. Although the latter two patents teach procedures which may be repeatedly used without exposing the tumor, risk of infection and healthy tissue damage remain ever present.
In "Method and Apparatus for Controlling and Optimizing the Heating Pattern for a Hyperthermia System," U.S. Pat. No. 4,397,314, issued to Victor A. Vaguine on Aug. 9, 1983, "Gapped Resonant Microwave Apparatus for Producing Hyperthermia Therapy of Tumors," U.S. Pat. No. 4,378,806, issued to Julian L. Henley-Cohn on Apr. 5, 1983, and "Deep Heating Electrode," U.S. Pat. No. 4,186,729, issued to William H. Harrison on Feb. 5, 1980, procedures are taught for the noninvasive heating of living tissue. However, there is little localization of the radiation and invasive temperature measurements are necessry to insure that healthy tissue is not heated excessively.
In "field Intensification in Radio Frequency Thermotherapy," U.S. Pat. No. 4,154,246, issued to Harry H. LeVeen on May 15, 1979, the inventor describes a tuned radio-frequency inductance element which may be implanted into the region of the tissue to be heated or inserted into any conveniently accessible tubular organ close thereto for intensifying the electromagnetic radiation impinging thereon supplied from an external source of such radiation which would otherwise be poorly directed and localized. There are no teachings therein of means for coupling the energy in the radio-frequency radiation impressed upon the implanted closed, resonant inductive circuit to the tissue to be heated. Indeed, the inventor has deliberately sought to minimize heating losses in the inductor by using copper or silver-coated copper as the inductor material. Moreover, there is no electrical contact between the resonant loop and the tissue since the implanted device is insulated. Therefore, any voltages generated thereon will not cause currents to flow in the adjacent tissue. Finally, the inductance element in LeVeen's patent may be buried deep within the body of the patient and consequently at a significant distance from the external source of radiation. That is, LeVeen does not teach close coupling between the external electromagnetic radiation source and the internally positioned closed resonant circuit.
Clearly then, an improved hyperthermia treatment of tumors would involve a noninvasive, well-localized procedure for heating tumors with specificity and temperature control. In the absence of suitable noninvasive procedures and the likelihood that the treatment will have to be repeated, an effective internally placed device would simplify the treatment and minimize the potential for infection.
Accordingly, an object of the present invention is to provide an apparatus for repeatedly heating tissue internal to a patient, locally and with significant specificity.
Another object of my invention is to provide an apparatus for repeatedly heating tissue internal to a patient, locally and with significant specificity without the danger thereto accompanying repeated surgical procedures to access the tissue to be heated, and without significant risk of infection and discomfort which accompanies the use of externally powered electrodes which must be inserted through the skin to apply radio-frequency energy to the tissue.
Yet another object of my invention is to provide an apparatus for the noninvasive measurement of the temperature of the tissue under treatment and for the control of the temperature therein.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.